Apple's iOS will continue its reign in the tablet market over the next four years, accounting for more than half of the OS share for this computing segment through to 2015, according to a new forecast.

In a statement Tuesday, Gartner predicted the iOS will power nearly 69 percent of all media tablets sold in 2011, led by the success of Apple's iPad. In 2015, it will command a 47 percent share of the market.

Google's Android OS, on the other hand, is set to increase its global share of the tablet market from 20 percent this year to about 39 percent in 2015, the analyst firm said.

Google's decision to not open up to third parties its tablet-optimized Honeycomb will prevent fragmentation but also slow the decline in price and eventually cap market share, said Roberta Cozza, principal analyst at Gartner, in the statement.

"Volume will be driven by support from many players, the ecosystem of applications for tablets getting more competitive and some platform flexibility allowing lower price points," he noted. "The new licensing model Google has introduced with Honeycomb enables Google to drive more control, allowing only optimal tablet implementations that don't compromise quality of experience.

"This might mean that prices will drop at a slower pace than what we have seen in the smartphone market."

Touching on Research In Motion's QNX platform, which powers the vendor's Blackberry Playbook, Gartner said the migration of Blackberry handsets to the OS by 2012 will offer customers a consistent experience across RIM's product portfolio. However, richness of ecosystem is key to achieving success in the media tablet market.

"It will take time and significant effort for RIM to attract developers and deliver a compelling ecosystem of applications and services around QNX to position it as a viable alternative to Apple or Android. This will limit RIM's market share growth over the forecast period," said Carolina Milanesi, research vice president at Gartner. "It will be mainly organizations that will be interested in RIM's tablets because they either already have RIM's infrastructure deployed or have stringent security requirements."

According to Gartner's forecast, QNX will have a 10 percent share of the tablet market by 2015.

Similarly, MeeGo and WebOS, which have a weak presence currently, have to grow their business in order to up their appeal, it pointed out.

Milanesi said: "Smartphone users will want to buy a tablet that runs the same operating system as their smartphone. This is so that they can share applications across devices as well as for the sense of familiarity the user interfaces will bring.

"Vendors developing on Android should be prepared to see more cross brand ownership as some users might put OS over brand when it comes to the purchasing decision. Improvements on usability and brand recognition are the strongest differentiators they can focus on."